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https://issues.apache.org/jira/browse/CURATOR-171?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15822946#comment-15822946
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Scott Blum commented on CURATOR-171:
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For what it's worth (this isn't a Curator issue), but in Solr I've frequent run
into problems as an administrator where a member's internal view of who the
leader is got out of sync with the actual queue. As an admin, I've desperately
wished each node would also watch its own registration. That way, if things
got out of whack (no leader, too many leaders) I could just delete all the
nodes and have everyone re-register and sort things out.
> LeaderLatch isn't aware if it's own ephemeral node goes away
> ------------------------------------------------------------
>
> Key: CURATOR-171
> URL: https://issues.apache.org/jira/browse/CURATOR-171
> Project: Apache Curator
> Issue Type: Bug
> Components: Recipes
> Reporter: John Vines
>
> Running the following code- {code} public static void main(String args[])
> throws Exception {
> CuratorFramework curator =
> CuratorFrameworkFactory.builder().connectString("localhost:2181").retryPolicy(new
> ExponentialBackoffRetry(1000, 5))
> .authorization("digest", "accumulo:DEFAULT".getBytes()).build();
> curator.start();
> LeaderLatch latch = new LeaderLatch(curator, "/latch", "test");
> LeaderLatch latch2 = new LeaderLatch(curator, "/latch", "test2");
> latch.addListener(new LeaderLatchListener() {
> @Override
> public void isLeader() {
> System.out.println("Became leader!");
> }
> @Override
> public void notLeader() {
> System.out.println("Lost leadership!");
> }
> });
> latch.start();
> latch.await();
> latch2.start();
> Thread.sleep(1000);
> System.out.println("Does latch1 have leadership? " +
> latch.hasLeadership());
> System.out.println("Does latch2 have leadership? " +
> latch2.hasLeadership());
> for (String child : curator.getChildren().forPath("/latch"))
> if (Arrays.equals(curator.getData().forPath(ZKPaths.makePath("/latch",
> child)), "test".getBytes()))
>
> curator.delete().deletingChildrenIfNeeded().forPath(ZKPaths.makePath("/latch",
> child));
> Thread.sleep(1000);
> System.out.println("Does latch1 have leadership? " +
> latch.hasLeadership());
> System.out.println("Does latch2 have leadership? " +
> latch2.hasLeadership());
>
> Thread.sleep(1000 * 40);
> System.out.println("Does latch1 have leadership? " +
> latch.hasLeadership());
> System.out.println("Does latch2 have leadership? " +
> latch2.hasLeadership());
>
> latch.close();
> latch2.close();
> curator.close();
> }{code}
> I get the following output-{noformat}Became leader!
> Does latch1 have leadership? true
> Does latch2 have leadership? false
> Does latch1 have leadership? true
> Does latch2 have leadership? true
> Does latch1 have leadership? true
> Does latch2 have leadership? true
> {noformat}
> I expect that when the ephemeral node is deleted, latch1 no longer reports
> itself as having leadership. Furthermore, I expect it to trigger the
> notLeader call.
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